Many existing medical devices includes tissue-penetrating elements. For example, U.S. Pat. No. 5,855,576 describes an ablation apparatus that includes a plurality of electrode tines (elongated electrodes) deployable from a cannula. Each of the tines includes a proximal end that is coupled to a generator, and a distal end that may project from a distal end of the cannula. When using the above described devices in percutaneous interventions, the cannula is generally inserted through a patient's skin to penetrate tissue, and the elongated electrodes are deployed out of the distal end of the cannula. The electrodes are then energized to ablate the target tissue.
It has been found that elongated electrodes have relatively low bending stiffness, thereby allowing the electrodes to easily bend during use. Sometimes, the bending of the electrodes may result in a deployed configuration of the electrodes within tissue that is not as that intended.
Also, sometimes it may be desirable to reposition the cannula and deploy the electrodes at a different location to create an additional lesion. For example, the cannula can be retracted and removed from the first target site, and reinserted into a new target site. However, such technique results in multiple puncture wounds and may increase the chance of metastasis resulted from cancer seeds migrating to other bodily locations through the puncture wounds. Sometimes, in order to minimize puncture wounds, a physician may attempt to turn or steer the distal end of the cannula (e.g., by applying a bending force at the proximal end of the cannula) to aim the distal end at different target tissue while the distal end is still inside the tissue. However, the cannula used to deploy the electrodes generally has relatively low bending stiffness, thereby preventing a physician from applying bending force at the proximal end of the cannula (e.g., applying a torque about an axis that is at an angle relative to an axis of the cannula).
Tissue-penetrating elements, such as medical needles, have also been used in a variety of applications. For examples, medical needles have been used to deliver substance, such as drug, contrast agent, diagnostic agent, and radioactive objects, to patients. Medical needles have also been used to collect substance, such as blood, tissue, or other bodily fluid, from a patient. In either case, the medical needle generally has a sharp distal tip for penetrating tissue, and is attached to a container in which the substance to be delivered or collected is stored. During use, the needle tip is used to pierce through a patient's skin to reach target site, and the substance is delivered to, or collected from, the target site via the needle.
Sometimes, in order to minimize the size of the wound at the patient's skin, the needle is made to have a circular cross-section having a small cross-sectional diameter. However, a needle with such configuration can bend easily as it is advanced into a patient's body, thereby resulting in the needle tip being inaccurately positioned.
Thus, there remains a need to provide for improved tissue-penetrating elements, such as elongated electrodes and medical needles, with good bending stiffness.